AutofillField has used the unique_name_ field to ensure that field could be identified without ambiguity (e.g., for filling later). The name is derived from the field's (HTML) name and some number suffix for uniqueness (in the FormStructure constructor).

Recently, AutofillField's parent, FormFieldData, got the unique_renderer_id data member, a 32-bit integer which identifies the field uniquely within a single renderer process. This ID is obtained from the DOM element (HTMLFormControlElement::unique_renderer_form_control_id_) and identifies the element for its whole lifespan.

It seems that AutofillField::unique_name_ can (and hence should) be replaced by FormFieldData::unique_renderer_id. This is the bug to track that work.